1. Field of the Invention
The present invention relates to improving the reliability of emergency power from uninterruptible power supplies.
2. Description of the Related Art
High reliability is often required in mission critical applications such as those that occur in medical, financial, communication, and military systems. Such systems can become very large and complex, involving numerous sub-systems that are integrated together by complex interconnections. For example, computer systems that process financial data can involve racks of hardware and can include hundreds of sub-systems, each with its own processors and power supplies. Another example is an Internet communication system that is comprised of numerous distributed servers. Such systems usually include a service processor that controls and integrates the individual sub-systems together under the direction of operating software.
Reliability can be so important that some systems have sub-systems with redundant power supplies that are connected to different power lines that are fed by different circuit-breakers. Other applications, e.g., communication servers, distribute user demands over distributed networks that are powered by different power lines that pass through different circuit breakers. Some applications are so critical that the different circuit-breakers are themselves powered by different power companies. However, no matter how reliable any power source is, it can fail. If dual-lines are fed from different circuit breakers powered by the same power company, the power company can fail. If different power companies are used, an electrical grid malfunction can shut-down both power companies.
While input power cannot be guaranteed, it is possible to provide protection by incorporating uninterruptible power supplies (UPS) devices into the system. A UPS device provides backup power in the event of an electrical outage or other power line disturbance. A UPS device usually includes a battery that powers an inverter that supplies operating power to the protected system or sub-system. The UPS device can either power the system or sub-system only when a failure occurs or it can power the system or sub-system continuously with the input AC power acting as a re-charger for the batteries.
UPS devices can provide sufficient power to operate a system for short periods of time, which can enable a controlled system shut-down to prevent, reduce, or mitigate problems. To improve reliability and/or to assist controlled shut-down it can be very useful to know what system resource is being powered by a particular UPS device and just how long power will be available. Then, if a UPS device signals that a power failure has or may occur the service processor can perform a controlled shut-down of impacted resources in time to protect data. Unfortunately, determining what system resource is connected to a particular UPS device and how long that device can reliably supply power becomes increasingly difficult as the number of UPS devices and system resources increase and as the protected system become more and more distributed. Complicating the problem is the desirability of determining which system resource is ultimately connected to a particular AC power line in a dual-line system.
Some dual-power line systems use only one UPS device that is fed from one AC power line. In such cases the other AC power line is directly connected to the other power line. In other dual-power line systems, each AC power line connects to a different UPS device. Either way, to maintain reliable operation it is important to ensure that each of the redundant power supplies is powered by a different AC power source. Otherwise, the purpose of having dual-power lines is defeated. It is also important that the UPS devices have sufficient capability to perform their intended tasks for the required period of time. That time period may be only long enough to protect data and to provide for an orderly system shut-down or it may extend until power can be restored or other measures are taken to keep the protected system operating. In a distributed system many different sub-systems are often connected to the same UPS device. If that UPS fails or if the UPS device does not have sufficient capability, those sub-systems can be brought down.
In the prior art a system designer would use manufacturer or test data to qualify particular UPS systems for particular applications. Installation personnel would then seek to ensure that the UPS devices are correctly installed. However, as systems become larger and as multiple UPS devices become more common it becomes increasingly difficult to ensure that a particular UPS device is suitable for its task. Complicating that problem is knowing what system or subsystem is actually being protected by a particular UPS device. Wiring errors or changes to a system over time can make it difficult to determine what is actually being protected. Determining whether a UPS device is suitable for its task is very difficult a as system expands over time, such as by adding new sub-systems, or changes over time, such as replacing an existing sub-system with a newer one. Dual line Cord Configurations add an additional layer of complexity due to the power supplies will draw half their max load during normal operation.
Therefore, techniques of identifying which system resource is connected to which UPS would be useful. Also useful would be a technique of automatically determining if a given UPS device is suitable for its task. Also useful would be a technique of enabling a system to automatically approximate how long a given UPS device can reliably supply power. Also beneficial would be a method of ensuring that sufficient notice is given before a particular UPS device fails to provide for a controlled system shut-down.